Pikachu is the player's guaranteed starter in Pokémon Yellow.
Unlike Pokémon Red and Blue, where the player chooses Bulbasaur, Charmander, or Squirtle, Pokémon Yellow gives the player Pikachu. This design was intended to reflect the Pokémon anime, in which Ash begins his journey with Pikachu rather than one of the traditional starter choices.
Pikachu follows the player around the overworld in Pokémon Yellow and reacts to the player's actions. The game also changes the rival's starting Pokémon: the rival begins with Eevee, which creates a different opening from the original Red and Blue storyline.
Pokémon Yellow was released in Japan in 1998 as an enhanced version of the first-generation games. It later reached North America in 1999 and Europe in 2000. Although Pikachu is mandatory at the beginning, players can still obtain the three original starter Pokémon during the adventure.